scope.html



<!DOCTYPE html>
<!--[if IE 8]><html class="no-js lt-ie9" lang="en" > <![endif]-->
<!--[if gt IE 8]><!--> <html class="no-js" lang="en" > <!--<![endif]-->
<head>
  <meta charset="utf-8">
  
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  
  <title>Design of Scope in Paddle &mdash; PaddlePaddle  documentation</title>
  

    <link rel="stylesheet" href="../_static/css/theme.css" type="text/css" />
  

        <link rel="index" title="Index"
              href="../genindex.html"/>
        <link rel="search" title="Search" href="../search.html"/>
    <link rel="top" title="PaddlePaddle  documentation" href="../index.html"/> 

  <link rel="stylesheet" href="https://cdn.jsdelivr.net/perfect-scrollbar/0.6.14/css/perfect-scrollbar.min.css" type="text/css" />
  <link rel="stylesheet" href="../_static/css/override.css" type="text/css" />
  <script>
  var _hmt = _hmt || [];
  (function() {
    var hm = document.createElement("script");
    hm.src = "//hm.baidu.com/hm.js?b9a314ab40d04d805655aab1deee08ba";
    var s = document.getElementsByTagName("script")[0]; 
    s.parentNode.insertBefore(hm, s);
  })();
  </script>

  
  <script src="../_static/js/modernizr.min.js"></script>

</head>

<body class="wy-body-for-nav" role="document">

  
  <header class="site-header">
    <div class="site-logo">
      <a href="/"><img src="../_static/images/PP_w.png"></a>
    </div>
    <div class="site-nav-links">
      <div class="site-menu">
        <a class="fork-on-github" href="https://github.com/PaddlePaddle/Paddle" target="_blank"><i class="fa fa-github"></i>Fork me on Github</a>
        <div class="language-switcher dropdown">
          <a type="button" data-toggle="dropdown">
            <span>English</span>
            <i class="fa fa-angle-up"></i>
            <i class="fa fa-angle-down"></i>
          </a>
          <ul class="dropdown-menu">
            <li><a href="/doc_cn">中文</a></li>
            <li><a href="/doc">English</a></li>
          </ul>
        </div>
        <ul class="site-page-links">
          <li><a href="/">Home</a></li>
        </ul>
      </div>
      <div class="doc-module">
        
        <ul>
<li class="toctree-l1"><a class="reference internal" href="../getstarted/index_en.html">GET STARTED</a></li>
<li class="toctree-l1"><a class="reference internal" href="../howto/index_en.html">HOW TO</a></li>
<li class="toctree-l1"><a class="reference internal" href="../api/index_en.html">API</a></li>
<li class="toctree-l1"><a class="reference internal" href="../mobile/index_en.html">MOBILE</a></li>
</ul>

        
<div role="search">
  <form id="rtd-search-form" class="wy-form" action="../search.html" method="get">
    <input type="text" name="q" placeholder="Search docs" />
    <input type="hidden" name="check_keywords" value="yes" />
    <input type="hidden" name="area" value="default" />
  </form>
</div>        
      </div>
    </div>
  </header>
  
  <div class="main-content-wrap">

    
    <nav class="doc-menu-vertical" role="navigation">
        
          
          <ul>
<li class="toctree-l1"><a class="reference internal" href="../getstarted/index_en.html">GET STARTED</a><ul>
<li class="toctree-l2"><a class="reference internal" href="../getstarted/build_and_install/index_en.html">Install and Build</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../getstarted/build_and_install/pip_install_en.html">Install Using pip</a></li>
<li class="toctree-l3"><a class="reference internal" href="../getstarted/build_and_install/docker_install_en.html">Run in Docker Containers</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/dev/build_en.html">Build using Docker</a></li>
<li class="toctree-l3"><a class="reference internal" href="../getstarted/build_and_install/build_from_source_en.html">Build from Sources</a></li>
</ul>
</li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../howto/index_en.html">HOW TO</a><ul>
<li class="toctree-l2"><a class="reference internal" href="../howto/usage/cmd_parameter/index_en.html">Set Command-line Parameters</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cmd_parameter/use_case_en.html">Use Case</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cmd_parameter/arguments_en.html">Argument Outline</a></li>
<li class="toctree-l3"><a class="reference internal" href="../howto/usage/cmd_parameter/detail_introduction_en.html">Detail Description</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../howto/usage/cluster/cluster_train_en.html">PaddlePaddle Distributed Training</a></li>
<li class="toctree-l2"><a class="reference internal" href="../howto/dev/new_layer_en.html">Write New Layers</a></li>
<li class="toctree-l2"><a class="reference internal" href="../howto/dev/contribute_to_paddle_en.html">Contribute Code</a></li>
<li class="toctree-l2"><a class="reference internal" href="../howto/dev/write_docs_en.html">Contribute Documentation</a></li>
<li class="toctree-l2"><a class="reference internal" href="../howto/deep_model/rnn/index_en.html">RNN Models</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../howto/deep_model/rnn/rnn_config_en.html">RNN Configuration</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../howto/optimization/gpu_profiling_en.html">Tune GPU Performance</a></li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../api/index_en.html">API</a><ul>
<li class="toctree-l2"><a class="reference internal" href="../api/v2/model_configs.html">Model Configuration</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/activation.html">Activation</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/layer.html">Layers</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/evaluators.html">Evaluators</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/optimizer.html">Optimizer</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/pooling.html">Pooling</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/networks.html">Networks</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/config/attr.html">Parameter Attribute</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../api/v2/data.html">Data Reader Interface and DataSets</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/data/data_reader.html">Data Reader Interface</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/data/image.html">Image Interface</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/data/dataset.html">Dataset</a></li>
</ul>
</li>
<li class="toctree-l2"><a class="reference internal" href="../api/v2/run_logic.html">Training and Inference</a></li>
<li class="toctree-l2"><a class="reference internal" href="../api/v2/fluid.html">Fluid</a><ul>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/layers.html">Layers</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/data_feeder.html">DataFeeder</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/executor.html">Executor</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/initializer.html">Initializer</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/evaluator.html">Evaluator</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/nets.html">Nets</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/optimizer.html">Optimizer</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/param_attr.html">ParamAttr</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/profiler.html">Profiler</a></li>
<li class="toctree-l3"><a class="reference internal" href="../api/v2/fluid/regularizer.html">Regularizer</a></li>
</ul>
</li>
</ul>
</li>
<li class="toctree-l1"><a class="reference internal" href="../mobile/index_en.html">MOBILE</a><ul>
<li class="toctree-l2"><a class="reference internal" href="../mobile/cross_compiling_for_android_en.html">Build PaddlePaddle for Android</a></li>
<li class="toctree-l2"><a class="reference internal" href="../mobile/cross_compiling_for_ios_en.html">PaddlePaddle Compiling Guide for iOS</a></li>
<li class="toctree-l2"><a class="reference internal" href="../mobile/cross_compiling_for_raspberry_en.html">Build PaddlePaddle for Raspberry Pi</a></li>
</ul>
</li>
</ul>

        
    </nav>
    
    <section class="doc-content-wrap">

      
<div role="navigation" aria-label="breadcrumbs navigation">
  <ul class="wy-breadcrumbs">
      
    <li>Design of Scope in Paddle</li>
  </ul>
</div>
      
      <div class="wy-nav-content" id="doc-content">
        <div class="rst-content">
          <div role="main" class="document" itemscope="itemscope" itemtype="http://schema.org/Article">
           <div itemprop="articleBody">
            
  <div class="section" id="design-of-scope-in-paddle">
<span id="design-of-scope-in-paddle"></span><h1>Design of Scope in Paddle<a class="headerlink" href="#design-of-scope-in-paddle" title="Permalink to this headline">¶</a></h1>
<div class="section" id="overview">
<span id="overview"></span><h2>Overview<a class="headerlink" href="#overview" title="Permalink to this headline">¶</a></h2>
<p>Scope is an important concept in programming languages, which defines a program region that a set of bindings between names and entities applies. In a specific scope, a valid name is uniquely associated with an entity, such as a variable. And in another scope, this name may refer to other entity or nothing at all. It clearly restricts the visibility and validity of names in a program. Hence <strong>Scope</strong> is introduced to PaddlePaddle to manage variables in context. But different from the original abstract concept, Scope now becomes an object with two important attributes:</p>
<ul class="simple">
<li>Scope is an association of a name to variable.</li>
<li>Variables in a parent scope can be retrieved from local scope.</li>
</ul>
<p>A detailed explanation of these two attributes goes as following.</p>
</div>
<div class="section" id="scope-is-an-association-of-a-name-to-variable">
<span id="scope-is-an-association-of-a-name-to-variable"></span><h2>Scope is an association of a name to variable.<a class="headerlink" href="#scope-is-an-association-of-a-name-to-variable" title="Permalink to this headline">¶</a></h2>
<p>Scope is an association of a name to variable. All variables belong to <code class="docutils literal"><span class="pre">Scope</span></code>. You need to specify a scope to run a Net, i.e., <code class="docutils literal"><span class="pre">net.Run(&amp;scope)</span></code>. One net can run in different scopes and update different variable in the scope.</p>
<ol>
<li><p class="first">Scope only contains a map of a name to variable.</p>
<p>All parameters, data, states in a Net should be variables and stored inside a scope. Each op should get inputs and outputs to do computation from a scope, such as data buffer, state (momentum) etc.</p>
</li>
<li><p class="first">Variable can only be created by Scope and a variable can only be got from Scope. User cannot create or get a variable outside a scope. This is a constraints of our framework, and will keep our framework simple and clear.</p>
</li>
<li><p class="first">Scope only contains methods that are used to Create and Get Variables. Scope do not contain Operators and have no information to run them.
<code class="docutils literal"><span class="pre">Net</span></code> is designed to drive the computation and Scope only contains a map of variables. There is no computation logic inside a <code class="docutils literal"><span class="pre">Scope</span></code>. Scope just handles the lifetime management of variables.</p>
<ul class="simple">
<li><code class="docutils literal"><span class="pre">Create</span></code> is used to create a Variable by its name and add the mapping relation.</li>
<li><code class="docutils literal"><span class="pre">Get</span></code> is used to find a Variable by name.</li>
</ul>
</li>
<li><p class="first">Every variable only belongs to one certain Scope.</p>
<p>Variable can not belong to many scopes. If you want to use variables from parent scope, you can use <code class="docutils literal"><span class="pre">parent</span> <span class="pre">scope</span></code>.</p>
</li>
<li><p class="first">Scope should destruct all Variables inside it when itself is destructed. User can never store <code class="docutils literal"><span class="pre">Variable</span></code> pointer somewhere else.</p>
<p>Because Variable can only be got from Scope. When destroying Scope, we also need to destroy all the Variables in it. If user store <code class="docutils literal"><span class="pre">Variable</span></code> pointer to private data member or some global variable, the pointer will be an invalid pointer when associated <code class="docutils literal"><span class="pre">Scope</span></code> is destroyed.</p>
</li>
</ol>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Scope</span> <span class="p">{</span>
 <span class="k">public</span><span class="o">:</span>
  <span class="n">Variable</span><span class="o">*</span> <span class="n">Var</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&amp;</span> <span class="n">name</span><span class="p">);</span>
  <span class="k">const</span> <span class="n">Variable</span><span class="o">*</span> <span class="nf">FindVar</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&amp;</span> <span class="n">name</span><span class="p">)</span> <span class="k">const</span><span class="p">;</span>

 <span class="k">private</span><span class="o">:</span>
    <span class="n">std</span><span class="o">::</span><span class="n">unordered_map</span><span class="o">&lt;</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o">&lt;</span><span class="n">Variable</span><span class="o">&gt;&gt;</span> <span class="n">vars_</span><span class="p">;</span>
<span class="p">};</span>
</pre></div>
</div>
</div>
<div class="section" id="parent-scope-and-local-scope">
<span id="parent-scope-and-local-scope"></span><h2>Parent scope and local scope<a class="headerlink" href="#parent-scope-and-local-scope" title="Permalink to this headline">¶</a></h2>
<p>Just like <a class="reference external" href="https://en.wikipedia.org/wiki/Scope_(computer_science)">scope</a> in programming languages, <code class="docutils literal"><span class="pre">Scope</span></code> in the neural network can also be a local scope. There are two attributes about local scope.</p>
<ol class="simple">
<li>We can create local variables in a local scope. When that local scope is destroyed, all local variables should also be destroyed.</li>
<li>Variables in a parent scope can be retrieved from local scopes of that parent scope, i.e., when user get a variable from a scope, it will try to search this variable in current scope. If there is no such variable in the local scope, <code class="docutils literal"><span class="pre">scope</span></code> will keep searching from its parent, until the variable is found or there is no parent.</li>
</ol>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Scope</span> <span class="p">{</span>
 <span class="k">public</span><span class="o">:</span>
  <span class="n">Scope</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">Scope</span><span class="o">&gt;&amp;</span> <span class="n">scope</span><span class="p">)</span><span class="o">:</span> <span class="n">parent_</span><span class="p">(</span><span class="n">scope</span><span class="p">)</span> <span class="p">{}</span>

  <span class="n">Variable</span><span class="o">*</span> <span class="n">FindVar</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&amp;</span> <span class="n">name</span><span class="p">)</span> <span class="k">const</span> <span class="p">{</span>
    <span class="k">auto</span> <span class="n">it</span> <span class="o">=</span> <span class="n">vars_</span><span class="p">.</span><span class="n">find</span><span class="p">(</span><span class="n">name</span><span class="p">);</span>
    <span class="k">if</span> <span class="p">(</span><span class="n">it</span> <span class="o">!=</span> <span class="n">vars_</span><span class="p">.</span><span class="n">end</span><span class="p">())</span> <span class="p">{</span>
      <span class="k">return</span> <span class="n">it</span><span class="o">-&gt;</span><span class="n">second</span><span class="p">.</span><span class="n">get</span><span class="p">();</span>
    <span class="p">}</span> <span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">parent_</span> <span class="o">!=</span> <span class="k">nullptr</span><span class="p">)</span> <span class="p">{</span>
      <span class="k">return</span> <span class="n">parent_</span><span class="o">-&gt;</span><span class="n">FindVar</span><span class="p">(</span><span class="n">name</span><span class="p">);</span>
    <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
      <span class="k">return</span> <span class="k">nullptr</span><span class="p">;</span>
    <span class="p">}</span>
  <span class="p">}</span>

 <span class="k">private</span><span class="o">:</span>
  <span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">Scope</span><span class="o">&gt;</span> <span class="n">parent_</span> <span class="p">{</span><span class="k">nullptr</span><span class="p">};</span>
<span class="p">};</span>
</pre></div>
</div>
<p>In <code class="docutils literal"><span class="pre">Scope</span></code> class, there is a private data member called <code class="docutils literal"><span class="pre">parent_</span></code>. <code class="docutils literal"><span class="pre">parent_</span></code> is a smart pointer to its parent scope. When user <code class="docutils literal"><span class="pre">Get</span></code> a variable by its <code class="docutils literal"><span class="pre">name</span></code>, the <code class="docutils literal"><span class="pre">name</span></code> will be searched inside the current scope. If the variable cannot be found locally and parent scope is not a <code class="docutils literal"><span class="pre">nullptr</span></code>, the variable will be searched inside that parent scope. <code class="docutils literal"><span class="pre">parent_</span></code> pointer&#8217;s default value is <code class="docutils literal"><span class="pre">nullptr</span></code>. It means that the scope is a global scope when <code class="docutils literal"><span class="pre">parent_</span></code> is nullptr.</p>
<p>A local scope is very useful when we implement Recurrent Neural Network. Each timestep of an RNN should be a <code class="docutils literal"><span class="pre">Net</span></code>. Each <code class="docutils literal"><span class="pre">Net</span></code> of timestep (<code class="docutils literal"><span class="pre">StepNet</span></code> for short) should use an independent local scope. Just like variables in a while loop is inside a local scope in programming languages. By using a single <code class="docutils literal"><span class="pre">StepNet</span></code> and changing local scope, we can implement an RNN easily.</p>
</div>
</div>
<div class="section" id="interface-design">
<span id="interface-design"></span><h1>Interface Design<a class="headerlink" href="#interface-design" title="Permalink to this headline">¶</a></h1>
<div class="highlight-cpp"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Variable</span> <span class="p">{</span>
 <span class="k">private</span><span class="o">:</span>
  <span class="n">Variable</span><span class="p">()</span> <span class="o">=</span> <span class="k">default</span><span class="p">;</span>
  <span class="k">friend</span> <span class="k">class</span> <span class="nc">Scope</span><span class="p">;</span>
<span class="p">};</span>

<span class="k">class</span> <span class="nc">Scope</span> <span class="p">{</span>
 <span class="k">private</span><span class="o">:</span>
  <span class="n">Scope</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">Scope</span><span class="o">&gt;&amp;</span> <span class="n">parent</span> <span class="o">=</span> <span class="k">nullptr</span><span class="p">);</span>

 <span class="k">public</span><span class="o">:</span>
  <span class="k">static</span> <span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">Scope</span><span class="o">&gt;</span> <span class="n">Create</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">Scope</span><span class="o">&gt;&amp;</span> <span class="n">parent</span> <span class="o">=</span> <span class="k">nullptr</span><span class="p">);</span>

  <span class="c1">// return nullptr if not found.</span>
  <span class="n">Variable</span><span class="o">*</span> <span class="nf">FindVar</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&amp;</span> <span class="n">name</span><span class="p">)</span> <span class="k">const</span><span class="p">;</span>

  <span class="c1">// return if already contains same name variable.</span>
  <span class="n">Variable</span><span class="o">*</span> <span class="nf">Var</span><span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&amp;</span> <span class="n">name</span><span class="p">);</span>

 <span class="k">private</span><span class="o">:</span>
  <span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">Scope</span><span class="o">&gt;</span> <span class="n">parent_</span><span class="p">;</span>
  <span class="n">std</span><span class="o">::</span><span class="n">unordered_map</span><span class="o">&lt;</span><span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">unique_ptr</span><span class="o">&lt;</span><span class="n">Variable</span><span class="o">&gt;&gt;</span> <span class="n">vars_</span><span class="p">;</span>
<span class="p">};</span>
</pre></div>
</div>
<div class="section" id="only-scope-can-create-a-variable">
<span id="only-scope-can-create-a-variable"></span><h2>Only scope can create a variable<a class="headerlink" href="#only-scope-can-create-a-variable" title="Permalink to this headline">¶</a></h2>
<p>To ensure <code class="docutils literal"><span class="pre">only</span> <span class="pre">scope</span> <span class="pre">can</span> <span class="pre">create</span> <span class="pre">a</span> <span class="pre">variable</span></code>, we should mark <code class="docutils literal"><span class="pre">Variable</span></code>&#8216;s constructor as a private member function, and Scope is a friend class of Variable. And then only <code class="docutils literal"><span class="pre">Var</span></code> can construct <code class="docutils literal"><span class="pre">Variable</span></code>.</p>
</div>
<div class="section" id="when-scope-destroyed-all-variables-inside-this-scope-should-be-destroyed-together">
<span id="when-scope-destroyed-all-variables-inside-this-scope-should-be-destroyed-together"></span><h2>When scope destroyed, all variables inside this scope should be destroyed together<a class="headerlink" href="#when-scope-destroyed-all-variables-inside-this-scope-should-be-destroyed-together" title="Permalink to this headline">¶</a></h2>
<p>The scope hold unique pointers for all variables. User can <code class="docutils literal"><span class="pre">FindVar</span></code> from scope, but he should not hold this pointer as a member variable. Because when scope is destroyed, all variables inside this scope will be destroyed together.</p>
</div>
<div class="section" id="sharing-a-parent-scope">
<span id="sharing-a-parent-scope"></span><h2>Sharing a parent scope<a class="headerlink" href="#sharing-a-parent-scope" title="Permalink to this headline">¶</a></h2>
<p>Local scope contains a <code class="docutils literal"><span class="pre">parent_</span></code> pointer. It is a linked-list for scopes. Using a <code class="docutils literal"><span class="pre">shared_ptr</span></code> because when a local scope is using, its parents cannot be destroyed.</p>
<p>Also, as the parent scope is a <code class="docutils literal"><span class="pre">shared_ptr</span></code>, we can only <code class="docutils literal"><span class="pre">Create()</span></code> a scope shared pointer. We cannot construct a scope variable, because it cannot be passed to other scope as <code class="docutils literal"><span class="pre">parent</span></code> pointer.</p>
</div>
<div class="section" id="orthogonal-interface">
<span id="orthogonal-interface"></span><h2>Orthogonal interface<a class="headerlink" href="#orthogonal-interface" title="Permalink to this headline">¶</a></h2>
<p><code class="docutils literal"><span class="pre">FindVar</span></code> will return <code class="docutils literal"><span class="pre">nullptr</span></code> when <code class="docutils literal"><span class="pre">name</span></code> is not found. It can be used as <code class="docutils literal"><span class="pre">Contains</span></code> method. <code class="docutils literal"><span class="pre">Var</span></code> will return an <code class="docutils literal"><span class="pre">Error</span></code> when there is a name conflict locally. Combine <code class="docutils literal"><span class="pre">FindVar</span></code> and <code class="docutils literal"><span class="pre">Var</span></code>, we can implement <code class="docutils literal"><span class="pre">Var</span></code> easily.</p>
</div>
</div>


           </div>
          </div>
          <footer>
  

  <hr/>

  <div role="contentinfo">
    <p>
        &copy; Copyright 2016, PaddlePaddle developers.

    </p>
  </div>
  Built with <a href="http://sphinx-doc.org/">Sphinx</a> using a <a href="https://github.com/snide/sphinx_rtd_theme">theme</a> provided by <a href="https://readthedocs.org">Read the Docs</a>. 

</footer>

        </div>
      </div>

    </section>

  </div>
  

    <script type="text/javascript">
        var DOCUMENTATION_OPTIONS = {
            URL_ROOT:'../',
            VERSION:'',
            COLLAPSE_INDEX:false,
            FILE_SUFFIX:'.html',
            HAS_SOURCE:  true,
            SOURCELINK_SUFFIX: ".txt",
        };
    </script>
      <script type="text/javascript" src="../_static/jquery.js"></script>
      <script type="text/javascript" src="../_static/underscore.js"></script>
      <script type="text/javascript" src="../_static/doctools.js"></script>
      <script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.0/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
       
  
    <script type="text/javascript" src="../_static/js/theme.js"></script>
  
  
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
  <script src="https://cdn.jsdelivr.net/perfect-scrollbar/0.6.14/js/perfect-scrollbar.jquery.min.js"></script>
  <script src="../_static/js/paddle_doc_init.js"></script> 

</body>
</html>